The present invention relates to an electrochemical generator apparatus and method, and in particular to electrochemical cells, such as primary cells, secondary batteries, and fuel cells, which use an appreciably strong acceleration force, generated by a centrifugal rotor, for improving efficiency of the apparatus and for controlling the electrochemical reactions within the apparatus.
The nickel-zinc (Ni-Zn) secondary battery, invented during the last century, has been the subject of continual development efforts because it offers more than double the energy density of the more often used lead-acid battery and because its materials are less toxic, reasonably inexpensive, and abundantly available. The major disadvantage of the Ni-Zn battery, compared to the leadacid battery, has been its short life, that is, the low number of effective charge-discharge cycles when compared to the lead-acid battery. Thus while the nickel electrode can be repeatedly charged and discharged thousands of times, the zinc electrode life, in spite of all prior efforts for improvement, has limited the operating life of this type of battery to about 200 chargedischarge cycles. This short life is totally inadequate, for instance, as an energy source for an electric car.
The short life is due to the high solubility of zinc in the electrolyte (an aqueous potassium hydroxide (KOH) solution) which, on the charge portion of the cycle, leads to uneven deposition and the growth of needle-like dendritic crystals which grow toward the nickel electrode and ultimately will cause an internal short circuit in the cell. One, and perhaps the only, prior Ni-Zn battery construction which has been operated for over 1000 charge-discharge cycles is the "Vibrocell" battery, described in U.S. Pat. No. 3,923,550. This battery employs a sparse plastic web as the separator. All zinc electrodes are driven in a fast reciprocating vertical movement by mechanical means. This construction achieves a turbulent electrolyte flow in the vicinity of the zinc surface, and the zinc electrode is charged by the formation of a compact zinc layer.
The drawbacks of the embodiment described above are created (a) by the structures in each separate cell which require considerable mechanical strength, (b) by the extra weight and energy loss caused by the shaker machinery, (c) by the heavy current collecting bolts needed for each cell, with which the cells are connected in series by moving interconnect cables, and (d) by the need for separate electrolyte quantity control for each cell. This cell structure further has a high self-discharge rate that quickly leads to the complete discharge of a fully charged battery.
Thus far, therefore, Ni-Zn batteries of bipolar construction have not been successfully devised.
Objects of the present invention are to remove the disadvantages noted above and to realize a new electrochemical generator and method which is reliable, efficient, and has a large number of charge-discharge cycles in a Ni-Zn battery structure.